id: design: pure-package import policy — package classes per tier, with compile-fail fixtures

Part of the worlds design program: #5955. Wave-2 follow-up from the prior-art research (Lane B item 2); parent topic issue: #5956. Research source: workspace/scratch/worlds-capabilities-brief-2026-11-04/prior-art-research.md.

Scope

Define which package classes a world/library may import at each tier, and pin the policy with fixtures:

Pure packages (parsers, unicode, random — no effects) compose freely; effect-referencing packages work only where the platform exposes the operations they call. Roc's model already enforces this by construction: if a library calls Stdout.line and the platform doesn't expose Stdout, it does not compile — there is no ambient I/O to fall back to (Roc FAQ: https://www.roc-lang.org/faq).
The policy table states, per tier: which classes are allowed, what the author must declare, and what the import checker verifies against the platform catalog (pkgs/id/crates/id-core/src/world_caps.rs).
One compile-fail fixture per class (a package in the class, a platform that must reject it), wired so the fixtures cannot silently rot — distinct from the single demo pair in the demo task under id: design program: worlds — advanced Roc libraries, capabilities, permissions, dynamic user functions, licensing (2026-11-04 brief) #5955, which proves the mechanism end-to-end.

Done looks like

A policy table (class × tier → allowed/declared/checked) plus the per-class compile-fail fixtures specified or landed.

CODE-1660

Triage — task 10360 (lane code-s)

Verdict: live design+fixtures issue, correctly scoped, nothing landed yet. Stays OPEN.

Evidence checked fresh 2026-11-05:

Issue id: design: pure-package import policy — package classes per tier, with compile-fail fixtures #5994 OPEN, no hard-stop labels. Parent topic id: design: Roc library imports for worlds — pure dependencies and platform-dependent dependencies #5956 (Roc library imports for worlds) OPEN; program parent id: design program: worlds — advanced Roc libraries, capabilities, permissions, dynamic user functions, licensing (2026-11-04 brief) #5955 OPEN.
Not already done: at origin/main there are NO compile-fail / import-policy fixtures under pkgs/id (fixture files present are transcript/relay/determinism fixtures and one wasm screen fixture — none pins an import class rejection), and no policy table exists. The checker target it names is real: pkgs/id/crates/id-core/src/world_caps.rs (catalog + ceilings, verified this shift under task 10327).
Mechanism premise is sound as filed: Roc's no-ambient-I/O model means an effect-referencing package fails to compile against a platform that doesn't expose the operation — the policy is a table + checker + fixtures over an existing enforcement shape, not new machinery.

Ordering recorded:

The per-tier columns depend on the tier definitions in the capability model id: design: capability model — requested vs discovered-used sets, registry listing, custom-compiled platforms #5958 (triaged today, task 10327) — including Drew's C2 ruling (default isolated tier unchanged; file/network capabilities are a new opt-in tier). The policy table should be written against those tiers, not invented locally.
Distinct from the id: design program: worlds — advanced Roc libraries, capabilities, permissions, dynamic user functions, licensing (2026-11-04 brief) #5955 demo pair (mechanism proof) — this issue's fixtures are per-class policy pins; keep them separate as filed.

No follow-up task enqueued — this issue is itself the work item and is in the queue system. Task 10360 completes as triaged.

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id: design: pure-package import policy — package classes per tier, with compile-fail fixtures #5994

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Done looks like

Triage — task 10360 (lane code-s)

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id: design: pure-package import policy — package classes per tier, with compile-fail fixtures #5994

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Done looks like

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developing-today commented on Nov 5, 2026

dezren39 commented on Nov 5, 2026

Triage — task 10360 (lane code-s)

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